Reviewed impact of pesticides, fertilizers on amphibians

Tadpoles can encounter runoff from pesticides and fertilizers while developing in bodies of water.

Photo by Lynn Ketchum

Common pesticides and fertilizers can damage both the development and survival of amphibians to varying degrees, according to a new analysis by Oregon State University.

The new meta-analysis marks the first attempt at a large-scale summary on the negative effects of specific chemical classes on amphibians, said Tiffany Garcia, a co-author of the study and an associate professor of wildlife science within OSU’s College of Agricultural Sciences. Researchers reviewed more than 150 scientific studies detailing the impacts of pesticides and fertilizers on amphibians.

Around 30 percent of amphibian species are now extinct or endangered due to a range of factors, including habitat loss, disease, and exposure to contaminants, including pesticides and fertilizers, according to Garcia.

"Billions of tons of agrochemicals are used in farming every year," said Garcia, an expert in aquatic ecology. "Any disruption to frog, toad and salamander communities has clear negative impacts on biodiversity and can also set off a domino effect throughout the ecosystem by damaging the food base for amphibian predators, including birds, snakes and fish."

Amphibians are also valuable to the environment as grazers, herbivores and predators of pests, such as mosquitos, she added.

Four classes of common agrochemicals significantly reduce amphibian survival, the researchers say: chloropyridinyls; inorganic fertilizers; carbamates, which are common in insecticides; and triazines, used in herbicides. Two others both kill and inhibit animal growth: phosphonoglycines and organophosphates, standard ingredients in many pesticides.

Agrochemicals are most damaging to amphibians in the egg and larval stages, decreasing survivorship and making individuals more susceptible to predation and also hindering the production of offspring later in life. Amphibians are especially vulnerable to pesticides and fertilizers since they live on land and in water and can come into contact with agrochemicals by both direct exposure and runoff into aquatic systems.

To reduce the effects of pesticides and fertilizers on amphibians, timing is critical.

"Farmers can be, and often are, the best naturalists we have," Garcia said. "Mixing agricultural production with wildlife management is vital to the survival of amphibians, especially with agricultural intensity growing to feed our booming global human population."

"Spring, for example, is a time with heavy agricultural application, and it's also when amphibians lay eggs and develop as larvae and tadpoles,” she added. "By modifying application schedules, growers can limit contact between sensitive wildlife species and harmful chemicals."

Former OSU graduate student Nick Baker led the meta-analysis, with assistance from Garcia and Betsy Bancroft of Southern Utah University.

The study was published earlier this year in the journal Science of the Total Environment and was funded by the Oregon Department of Fisheries and Wildlife at OSU, as well as a grant from the U.S. Department of Agriculture Conservation Effects Assessment Project.